Method and apparatus for performing random access procedures

ABSTRACT

A mobile terminal and a method of performing a random access procedure by the terminal is achieved by transmitting a random access preamble to a base station, receiving a random access response from the base station, and performing an uplink transmission using an uplink grant from the base station. The uplink transmission is performed by using a maximum number of HARQ (Hybrid Automatic Repeat reQuest) transmissions parameter, which is included in a System Information Block (SIB) received from the base station.

CROSS-REFERENCE

The present application claims priority benefit to the followingapplications, which contents are all incorporated by reference herein:U.S. Provisional Application Nos. 61/044,558 (filed Apr. 14, 2008) and61/047,736 (filed Apr. 24, 2008), and Korean Patent Application No.10-2009-0031965 (filed Apr. 13, 2009).

BACKGROUND

The present invention relates to a method for performing random accessprocedures. In the related art, random access procedures were performed,but radio resources were unnecessarily wasted. As such, the related arttechnologies do not sufficiently address such issues, and thus do notoffer appropriate solutions.

SUMMARY

The present inventors recognized at least the above-identified drawbacksof the related art. Based upon such recognition, the various featuresdescribed hereafter have been conceived such that a method of performingrandom access procedures is provided, which results in more efficientuse of radio resources.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary network architecture of an Evolved UniversalMobile Telecommunications System (E-UMTS).

FIG. 2 shows an exemplary control plane radio interface protocol stackused between a UE and an eNB.

FIG. 3 shows an exemplary user plane radio interface protocol stack usedbetween a UE and an eNB.

FIG. 4 shows an exemplary flow chart of a contention based random accessprocedure between a UE and eNB.

FIG. 5 shows an exemplary relationship between the PDCCH and PDSCH,which are channels from the eNB to the UE.

FIG. 6 shows some exemplary HARQ operations between the eNB and UE.

FIG. 7 shows an exemplary flow chart according to the present invention.

FIG. 8 shows an exemplary signal flow diagram of a contention basedrandom access procedure between the UE and eNB.

FIG. 9 shows another exemplary signal flow diagram of a contention basedrandom access procedure between the UE and eNB.

DETAILED DESCRIPTION

The inventive concepts and features herein related to a method forperforming random access procedures are explained in terms of a LongTerm evolution (LTE) system or other so-called 4 G communicationsystems, which is an enhancement to current 3GPP technologies. However,such details are not meant to limit the various features describedherein, which are applicable to other types of mobile and/or wirelesscommunication systems and methods.

Hereafter, the term “mobile terminal” will be used to refer to varioustypes of user devices, such as mobile communication terminals, userequipment (UE), mobile equipment (ME), and other devices that supportvarious types of wireless communication technologies.

Second generation (2G) mobile communications relate to transmitting andreceiving voice signals in a digital manner, and include technologiessuch as CDMA, GSM, and the like. As an enhancement from GSM, GPRS wasdeveloped to provide packet switched data services based upon GSM.

Third generation (3G) mobile communications relate to transmitting andreceiving not only voice signals, but also video and data. The 3GPP(Third Generation Partnership Project) developed the IMT-2000 mobilecommunication system and selected WCDMA as its radio access technology(RAT). The combination of IMT-2000 and WCDMA can be referred to as UMTS(Universal Mobile Telecommunications System), which comprises a UMTSTerrestrial Radio Access Network (UTRAN).

As data traffic is expected to increase dramatically, thestandardization for 3^(rd) generation mobile communications is underwayto establish a Long-Term Evolution (LTE) network that supports greaterbandwidth. LTE technologies are employed for an Evolved-UMTS (E-UMTS),which has an Evolved-UTRAN (E-UTRAN) that uses OFDMA (OrthogonalFrequency Division Multiple Access) as its radio access technology(RAT).

FIG. 1 shows the network architecture of an Evolved Universal MobileTelecommunications System (E-UMTS).

As can be understood from FIG. 1, the E-UMTS is a system that hasevolved from UMTS and its basic standardization is currently beingperformed by the 3GPP organization. The E-UMTS system is also referredto as an LTE (Long-Term Evolution) system.

The E-UMTS network can be basically divided into the E-UTRAN and the CN(core network). The E-UTRAN includes a mobile terminal (User Equipment:UE) 10, a base station (eNode B: eNB) 21, 22, 23 (all referred to as20), a serving gateway (S-GW) 31 located at the end of the network andconnected to external networks, and a Mobility Management Entity (MME)32 that oversees the mobility of the mobile terminals. For a singleeNode B 20, one or more cells may exist.

FIG. 2 shows an exemplary control plane radio interface protocol stackused between a UE and an eNB, and FIG. 3 shows an exemplary user planeradio interface protocol stack used between a UE and an eNB.

Such radio interface protocol is based upon the 3GPP radio accessnetwork standard, and is horizontally divided into a physical layer, adata link layer and a network layer, while vertically divided into auser plane for transmitting data information and a control plane fortransferring control signaling.

The protocol layers are based on the lower 3 layers of the Open SystemInterconnection (OSI) standard model, and are divided into a first layer(L1), a second layer (L2), and a third layer (L3).

Hereafter, each layers in the control plane radio protocol of FIG. 2 andin the user plane radio protocol of FIG. 3 will be explained.

L1 (Layer 1) is a physical layer (PHY) that uses physical channels toprovide an information transfer service to upper layers. The PHY layeris connected to an upper layer (the MAC layer) via transport channelsthrough which data is transferred between the MAC layer and the PHYlayer. Also, between respectively different physical layers (i.e.between physical layers in the transmitting side and in the receivingside), data is transferred through the physical channels.

The physical channels that exist for the physical layer in thetransmitting side and in the receiving side include: SCH(Synchronization Channel), PCCPCH (Primary Common Control PhysicalChannel), SCCPCH (Secondary Common Control Physical Channel), DPCH(Dedicated Physical Channel), PICH (Paging Indicator Channel), PRACH(Physical Random Access Channel), PDCCH (Physical Downlink ControlChannel) and PDSCH (Physical Downlink Shared Channel) and the like.

The MAC (Media Access Control) layer provides services to an upperlayer, namely the RLC (Radio Link Control) layer via logical channels.Here, based upon the type of data being transmitted, the logicalchannels can be divided into control channels that are used to transmitcontrol plane data, and traffic channels that are used to transmit userplane data.

In L2 (Layer 2), the RLC (Radio Link Control) layer is responsible forsupporting the transmission of data with reliability. Each radio bearer(RB) is responsible to the guarantee of QoS (Quality of Service) andtransmits data accordingly. In order to guarantee the QoS that is uniqueto the RB, one or two independent RLC entities are provided for each RB,and three types of RLC modes (TM: Transparent Mode, UM: UnacknowledgedMode, and AM: Acknowledged Mode) are provided to support various QoS.

In L2 (Layer 2), the PDCP layer performs a header compression functionto allow effective transmission of IP packets (such as IPv4 and IPv6)over the radio interface having relatively small bandwidth, by reducingthe size of IP packet headers that contain relatively large andunnecessary control information. Also, the PDCP layer is used to performencoding of control plane (C-plane) data, such as RRC messages. The PDCPlayer can also perform encoding of user plane (U-plane) data as well.

Located at the topmost region of L3 (Layer 3), the RRC (Radio ResourceControl) layer is defined only in the control plane, and handles theconfiguration, re-configuration and release of radio bearers (RBs) andhandles the control of logical channels, transport channels, andphysical channels associated thereto.

Here, the RB refers to a service provided by Layer 2 to transfer databetween the UE and the E-UTRAN.

Among the transport channels, there is a RACH (Random Access Channel)which is used to transmit data having relatively short length via theuplink. In particular, the RACH is used when a terminal, which has notbeen allocated any dedicated radio resources, has a signaling message oruser data that needs to be transmitted via the uplink, or is used whenthe base station (eNB) indicates to the terminal that a ransom accessprocedure is to be performed.

Hereafter, the random access procedure provided in an LTE system will beexplained in more detail.

The terminal performs a random access procedure in the followingexemplary situations:

-   -   when the terminal performs an initial connection with the base        station if there is no connection (RRC connection);    -   when the terminal first accesses the target cell in the handover        procedure;    -   when requested by a command from the base station;    -   if time synchronization of the uplink does not match, or the        designated radio resources to be used for requesting radio        resources have not been allocated, but when data of the uplink        is generated; and    -   recovery procedure when there is a radio link failure or        handover failure.

In the LTE system, such random access procedures can be divided into acontention based random access procedure and a non-contention basedrandom access procedure. Such division depends upon whether the randomaccess preamble used during the random access procedure is selected bythe terminal itself or selected by the base station.

In the non-contention based random access procedure, the terminal usesthe random access preamble that was directly allocated to it by the basestation. Thus, when the base station allocates a particular randomaccess preamble to the terminal, only that terminal uses such randomaccess preamble, and other terminals do not use this random accesspreamble. Thus, because the random access preamble and the terminalusing that random access preamble have a 1:1 relationship, it can besaid that there are no collisions (or contentions). In such case, assoon as such random access preamble is received by the base station, theterminal that transmitted the random access preamble can be known, andsuch procedures are efficient.

In contrast, in the contention based random access procedure, among aplurality of random access preambles that the terminal can use, one israndomly chosen and transmitted, and thus there is the possibility thata plurality of terminals may use the same random access preamble. Thus,upon receiving a particular random access preamble, the base stationcannot know which terminal transmitted such random access preamble.

FIG. 4, which shows a flow chart of the contention based random accessprocedure between the terminal and the base station, will be referred toin order to explain about the contention based random access procedure.

1) First, in the contention based random access procedure, based uponthe indication of a group of random access preambles provided throughsystem information or a handover command, the terminal randomly selectsone random access preamble, then selects the PRACH resources that can beused to transmit such random access preamble, and performs transmission.

Here, the preamble may be referred to as RACH MSG 1. If the terminalitself selects the preamble at random, such is called a contention basedRACH procedure, and such selected preamble is called a contention basedpreamble. Meanwhile, if the terminal is allocated a preamble from thenetwork via the RRC or the PDCCH, this is called a non-contention basedRACH procedure, and the preamble is called a dedicated preamble.

2) After transmitting the random access preamble in the above manner,the terminal attempts to receive its random access response within arandom access response reception window that was indicated by systeminformation or handover command from the base station.

In more detail, random access response information (i.e. RACH MSG 2) istransmitted as a MAC PDU (Protocol Data Unit) format, and such MAC PDUis transferred via a PDSCH (Physical Downlink Shared Channel). Namely,in order to allow the terminal to appropriately receive the informationtransferred over the PDCCH, control information is also transferred tothe terminal through the PDCCH (Physical Downlink Control Channel).Namely, the PDCCH information includes information about the terminalthat needs to receive the PDSCH, the frequency and time information forthe radio resources of the PDSCH, and the transmission formation of thePDSCH, and the like.

If the terminal succeeds in receiving the PDCCH, then the random accessresponse sent via the PDSCH can be appropriately received according tothe information of the PDCCH. Here, the random access response includesvalues such as a preamble identifier (ID), a UL Grant (uplink radioresources), a temporary C-RNTI (Radio Network Temporary Identifier), anda time alignment command, and the like. Here, if a random accesspreamble identifier is needed, and because ransom access responseinformation intended for one or more terminals can be included in asingle random access response, the UL grant, temporary C-RNTI, and TimeAlignment Command information are used to inform about the terminal forwhich such information is valid. The random access preamble identifieris the same as the random access preamble that was selected in theprocedures mentioned above. In the procedure 1) above, if the dedicatedpreamble was used, and if MSG 2 included a corresponding response, theransom access procedure is ended.

3) If the terminal receives a random access response that is valid foritself, the information included in the random access response isprocessed respectively.

Namely, the terminal applies the Time Alignment Command, and stored thetemporary C-RNTI. Also, by using the UL Grant, the data stored in thebuffer of the terminal or newly generated data are transmitted to thebase station. Here, the data transmitted through the UL Grant, namelythe MAC PDU is commonly referred to as a RACH MSG 3.

Among the data included in the UL Grant (also referred to as message 3),the identifier of the terminal should essentially be included. This isbecause the base station cannot determine which terminals performed therandom access procedure, identifying each terminal allows futurecollisions to be resolved.

Here, there are two ways to include a terminal identifier. First, If theterminal has a valid cell identifier that was allocated from thecorresponding cell before the random access procedure, the terminaltransmits its cell identifier through the UL Grant. However, if a validcell identifier was not allocated, the terminal performs transmission byincluded its own unique identifier (e.g. S-TMSI or Random ID). Ingeneral, such unique identifier is greater in length than the cellidentifier. If the terminal transmitted data through the UL Grant, acontention resolution timer is started.

4) After transmitting data that includes its identifier, through use ofthe UL Grant included in the random access response, the terminal waitsfor instructions from the base station for contention resolution (or toresolve any contention). Namely, an attempt to receive the PDCCH is madein order to receive a certain message.

There are two types of ways to receive the PDCCH. As describedpreviously, the first way is to attempt PDCCH reception by using thecell identifier, if the cell identifier is its identifier that wastransmitted via the UL Grant. The second way (i.e. if its identifier isa unique identifier) is to use the Temporary C-RNTI included in therandom access response in attempting to receive the PDCCH.

In the above first method, if the PDCCH (hereafter referred to asmessage 4) is received through its cell identifier before expiration ofthe contention resolution timer, the terminal determines that the randomaccess procedure was performed in a normal manner, and the random accessprocedure is ended. In the above second method, if the PDCCH wasreceived through the temporary cell identifier before expiration of thecontention resolution timer, the data within the PDSCH is checkedaccording to the indication of the PDCCH. The data (or MACH PDU) withinthe PDSCH is often referred to as PACH MSG 4. If the above data includesits unique identifier, the terminal determines that the random accessprocedure was performed normally, and the random access procedure isended.

Next, the method of receiving data (i.e. downlink data) by the terminalfrom the base station via a physical channel will be explained.

FIG. 5 shows the relationship between the PDCCH (Physical DownlinkControl Channel) and the PDSCH (Physical Downlink Shared Channel), whichare channels from the base station to the terminal.

As shown in FIG. 5, in the downlink from the base station to theterminal, there are basically two types of physical channels, PDCCH andPDSCH.

The PDCCH is not directly related to user data transmissions, but isused to send control information needed for managing physical channels.To put simply, it can be said that the PDCCH is used for controllingother physical channels. In particular, the PDCCH is used to transmitinformation needed by the terminal to receive the PDSCH. Informationabout the data having been transmitted at a particular point in time,using a certain frequency bandwidth, intended for certain terminals, thesize of such data and the like are transmitted via the PDCCH. Thus, eachterminal receives the PDCCH at a particular TTI (Transmit TimeInterval), and through the PDCCH, it is checked as to whether or not thedata to be received was transmitted, and if transmission of the datathat needs to be received is informed, the information such as thefrequency indicated by the PDCCH is used in receiving the PDSCH. Namely,it can be said that information specifying about which terminal (one ora plurality) should receive PDSCH data, how such terminal(s) shouldreceive and decode the PDSCH data, and the like are included in thePDCCH (Physical Downlink Control Channel).

For example, in a particular sub-frame, it is assumed that radioresources information A (e.g. frequency position) and transmissionformat information B (e.g. transport block size, modulation method,coding information, etc.) undergo CRC masking using information C (i.e.RNTI (Radio Network Temporary Identity)) and transmitted via the PDCCH.Here, one or more terminals in the corresponding cell use their RNTIinformation to monitor the PDCCH. As such, for a terminal having an RNTIof C, when the PDCCH is decoded, CRC errors do not occur. Thus, suchterminal employs the transport format information B and the radioresource information A to decode the PDSCH and receive data. Meanwhile,for any terminal that does not have an RNTI of C, CRC errors occur whenthe PDCCH is decoded. Thus, such terminal does not receive the PDSCH.

In the above procedures, in order to inform about how radio resourceswere allocated to which terminals, an RNTI (Radio Network TemporaryIdentifier) is transmitted and there are two types of RNTIs: dedicatedRNTIs and common RNTIs. A dedicated RNTI is allocated to a singleterminal, and is used for transmission and reception of datacorresponding to that terminal. The dedicated RNTI is allocated only toa terminal that had its information registered in the base station. Incontrast, a common RNTI is used by terminals that did not receiveallocation of a dedicated RNTI because its information was notregistered in the base station, but need to send and receive data withthe base station, or a common RNTI is used in transmitting information(such as system information) that commonly applies to a plurality ofterminals.

As described thus far, the E-UTRAN is comprised of two main elements: abase station and a terminal.

The radio resources for a single cell are comprised of uplink radioresources and downlink radio resources. The base station handles theallocation and control of uplink radio resources and downlink radioresources. Namely, the base station determines when and what radioresources are to be used by particular terminals. For example, the basestation can determine that 3.2 seconds from now, frequencies 100 MHz to101 MHz are to be allocated to user 1 to be used for a duration of 0.2seconds in downlink data transmissions. After the base station makessuch determination, this is informed o the terminal to allow downlinkdata reception thereof. Similarly, the base station also determines whenand how much of a certain radio resource should be used by a particularterminal(s) for uplink data transmissions, then informs the terminal(s)abut this determination such that these terminal(s) can use thedetermined radio resources for data transmissions.

Unlike in the related art, by having the base station dynamically manageradio resources, the effective use of radio resources is possible. Inthe related art, a single radio resource was continuously used by asingle terminal during a call connection. This is especiallyunreasonable considering that many recent services are IP packet based.This is because packet services do not generate packets in a continuousmanner during the duration of the call connection, and thus there aremany time periods where nothing is being transmitted. Despite this,continuously allocated radio resources for that single terminal is notefficient. To solve this issue, in the E-UTRAN system, radio resourcesare allocated to the terminal only when necessary and when service dataexists.

FIG. 6 shows some exemplary HARQ operations that may be performed in theMAC layer, and the HARQ operation details are as follows:

First, in order for the base station to transmit data to the terminal ina HARQ method, scheduling information is transmitted through a PDCCH(Physical Downlink Control Channel).

Such scheduling information may include terminal identifiers or terminalgroup identifiers (i.e. UE ID or Group ID), position of allocated radioresources (i.e. resource assignment), transmission parameters (i.e.modulation methods, payload size, MIMO related information, etc.), HARQprocess information, redundancy version, and new data indicators, andthe like.

The scheduling information is transferred through the PDCCH with respectto retransmissions, and the corresponding information may changeaccording to the channel environment. For example, if the channelenvironment has become better than that of initial transmission, themodulation method, payload size, etc. may be changed to allowtransmission at a higher bit rate, but if the channel environment hasbecome worse than that of initial transmission, then transmissions maybe performed at a lower bit rate.

2) The terminal monitors the control channel (PDCCH) at each TTI, andchecks the scheduling information that is received. If there is anyscheduling information pertaining to the terminal, data is received fromthe base station through the PSCH (Physical Shared Channel) at a timerelated to the PDCCH.

3) The terminal receives data and stores such in a soft buffer andattempts decoding of such data. Based upon the results of such decoding,HARQ feedback is provided to the base station. Namely, the terminalsends to the base station an ACK signal if decoding is successful or aNACK signal if decoding is unsuccessful.

4) If an ACK signal is received, the base station knows that datatransmission was successful and then transmits subsequent data. However,if a NACK signal is received, the base station knows that datatransmission was unsuccessful and the same data is retransmitted in thesame or different format at the appropriate time.

5) The terminal that sent the NACK signal, attempts reception of thedata that was retransmitted. The terminal can know whether thetransmitted data is an initial transmission or a retransmission ofprevious data by considering the NDI (New Data Indicator) in the PDCCH.

The NDI field is a one bit field that is toggled (0→1→0→1 . . . )whenever new data is transmitted, while the same bit value is used for aretransmission. Namely, the terminal compares whether the NDI field isthe same as that of the previous transmission to determine whether ornot a retransmission has been performed.

6) When the terminal receives retransmitted data, decoding thereof canbe attempted again by using various combinations of the data previouslystored in the soft buffer after unsuccessful decoding, and an ACK signal(upon successful decoding) or a NACK signal (upon unsuccessful decoding)is sent to the base station. The terminal may repeat the procedures ofsending NACK signals and receiving retransmissions until decoding issuccessful.

Thus far, HARQ in the downlink direction (from base station to terminal)was explained.

However, for the uplink direction (from terminal to base station),synchronous HARQ is employed. Here, synchronous HARQ refers to atechnique where the time interval for each data transmission is thesame. Namely, when the terminal should perform retransmission after anoriginal transmission, such retransmission occurs at a certain timeafter the original transmission. As such, using the same time intervalreduces any waste of radio resources that would be needed if schedulinginformation is transmitted using the PDCCH at various differentretransmission points of time, and also results in a decrease insituations where the terminal cannot perform appropriate retransmissionsbecause the PDCCH was not properly received.

In such synchronous HARQ procedure, values indicating the maximum numberof transmissions and the maximum number of retransmissions are used.

The maximum number of transmissions is a value that is one greater thanthe maximum number of retransmissions (i.e. Max. # of re-Tx=Max. # ofTx+1), and both values have the same purpose. Namely, these valuesindicate the maximum number of times that a particular data block can betransmitted (or retransmitted) through HARQ. A maximum number ofretransmissions is provided in order to minimize the delays orbottleneck in transferring data that would occur if retransmissions wereunlimited, and to consider the mobile communications environment thatrequires sharing of radio resources among multiple users.

If the terminal receives a NACK signal from the base station withrespect to its original transmission, retransmissions are performed andif the maximum number of retransmissions is reached (but stillunsuccessful), further transmission of the corresponding data is stoppedand such data is deleted from the buffer.

In the related art, for a terminal that is connected with a basestation, a value regarding the maximum number of transmissions isreceived. While a connection is established, the terminal continues touse such value to perform HARQ.

However, there are two ways that the terminal receives radio resourceallocation from the base station.

First, a dedicated identifier (i.e. C-RNTI) allocated to the terminal isused to receive allocation of radio resources through the PDCCH. Second,when the terminal receives allocation of radio resources through theRACH procedure (i.e. radio resources for transmitting a RACH MSG 3),radio resource allocation is received via a RACH MSG 2.

In the above first method, the base station is able to know what radioresources were allocated to which particular terminals. Thus, the basestation can allocate radio resources for a time considering the maximumnumber of transmissions set for each terminal.

However, in the above second method, the base station cannot know whatradio resources were allocated to which particular terminals. Thus, thebase station cannot know what terminals use the radio resources, andcannot know the maximum number of transmission set for each terminal,and thus there are problems in not being able to allocate the necessaryamount of radio resources to be used for certain time durations.

For example, if the maximum number of transmissions that was set for aterminal that actually uses a particular amount of radio resources isgreater than the maximum number of transmissions expected by the basestation, collisions in radio resources would occur. Also, if the maximumnumber of transmissions that was set for a terminal that actually uses aparticular amount of radio resources is less than the maximum number oftransmissions expected by the base station, the terminal does not useall of the radio resources allocated from the base station and thus awaste of radio resources occurs.

Thus, the present inventors recognized at least the above identifiedproblems, and provided the features of the present invention to solvesuch problems. Namely, an aspect of the present invention is to allowthe terminal to effectively use radio resources to performretransmissions. Also, by effectively using radio resources, collisionsof radio resources within a certain cell can be minimized.

Accordingly, the present invention provides a mobile terminal and amethod of performing a random access procedure by the terminal that isachieved by transmitting a random access preamble to a base station,receiving a random access response from the base station, and performingan uplink transmission using an uplink grant from the base station. Theuplink transmission is performed by using a maximum number of HARQ(Hybrid Automatic Repeat reQuest) transmissions parameter, which isincluded in a System Information Block (SIB) received from the basestation.

As a result of using the present invention, the terminal can effectivelyuse radio resources in performing retransmissions and radio resourcecollisions within a cell can be reduced.

The features described herein may be applied to an LTE system. However,such exemplary embodiments are not meant to be limiting, as thetechnical features of the present invention may be applied to varioustypes of mobile or wireless communication systems and techniques

The technical terms and phrases used herein are used to describefeatures in particular embodiments, and are not meant to limit theconcepts of the present invention. Also, if a technical term herein isnot specifically defined in a different manner, such will be interpretedto have the meaning that one of ordinary skill in the art wouldunderstand, without an excessively broad or excessively narrowinterpretation. If any terms herein have been erroneously used or notcompletely technically accurate, then such terms may be clarified orinterpreted as those skilled in the art would deem appropriate. Also,certain general terms used herein shall be interpreted according totheir dictionary meaning, or interpreted in view of the context withoutbeing construed too narrowly.

Also, any words or phrases used herein in the singular may beinterpreted to cover their plurality, unless clearly described to thecontrary. The word “including” or “comprising” or the like should not beinterpreted to mean that the various elements or steps always need to bepresent. Some elements or steps may not need to be present, oradditional elements or steps may also be present.

The words “first” or “second” or other terms that connote an order orsequence may be used to describe various different elements or steps toprovide distinguishing therebetween, unless specified that the numericalorder is of some significance. For example, without exceeding the scopeof the present invention, a first element can also be explained as asecond element, while a second element can also be explained as a firstelement.

For any description about one element being “connected to” or “connectedwith” or the like, with respect to another element, a direct connectionmay be possible or an intermediate element may exist between the twoelements. On the other hand, if two elements are described to be“directly” connected together, this may mean that no other elementsexists therebetween.

Hereafter, with reference to the attached drawings, some embodimentswill be explained, and regardless of the reference numbers in thedrawings, some elements may be labeled with the same reference numbersand any repetitive explanations may have been omitted merely for thesake of brevity. Also, certain aspects of the related or conventionalart, which may be a basis for the present invention, may have not beenexplained but could be understood by those skilled in the art. Thefeatures shown in the attached drawings are merely depicted to improvethe understanding of the present invention and should not be interpretedto limit the teachings of the present invention. As such, variousmodifications, changes, equivalents and replacements are part of theinventive features described throughout this description.

Hereafter, the term ‘mobile terminal’ is used, but can also be referredto US (User Equipment), ME (Mobile Equipment), MS (Mobile Station), andthe like. Also, a mobile terminal can include highly portable deviceshaving communication functions, such as a portable phone, a PDA, a SmartPhone, a notebook/laptop computer, etc., as well as less portabledevices, such as personal computers (PC), vehicle mounted devices, andthe like.

FIG. 7 shows an exemplary flow chart of a random access procedure forthe present invention.

As shown, with respect to a single cell, the base station sets a firstvalue for maximum number of transmissions for a HARQ that is commonlyused by all terminals (namely, a common value for maximum number oftransmissions), and includes such set first value into systeminformation, which is transmitted to the terminal. Here, the commonvalue for maximum number of transmissions can be included in the“max-HARQ-Msg3Tx” parameter. Also, the base station sets a second valuefor maximum number of transmissions (namely, a dedicated value formaximum number of transmissions), and includes such set second valueinto a dedicated message (or in a System Information Block: SIB), whichis transmitted to the terminal. Here, the dedicated value for maximumnumber of transmissions can be included in the “max-HARQ-Tx” parameter.

Then, the terminal obtains the dedicated maximum number of transmissionsand common maximum number of transmissions for HARQ (S110). Namely, theRRC layer in the terminal receives the dedicated maximum number oftransmissions included in the max-HARQ-Tx parameter and the commonmaximum number of transmissions included in the max-HARQpMsg3Txparameter, which are then transferred to the MAC layer.

Thereafter, in a state that dedicated radio resources have not yet beenreceived, when there is a signaling message or user data that needs tobe transmitted to the base station, the MAC layer in the terminalselects a RACH (Random Access Channel) Preamble, and transmits theselected preamble (RACH MSG 1) (S120). Here, not being allocated anydedicated radio resources means that the radio resources have not beenset such that only that terminal uses such radio resources. Namely, itmeans that a plurality of terminals may simultaneously use the radioresources. Or, it may mean that the radio resources have not beenallocated a terminal dedicated identifier (i.e. a C-RNTI). Or, it maymean that if the terminal received allocation of some radio resource,such radio resources were not set by semi-persistent scheduling (SPS).

In such case, the base station transmits control information through thePDCCH (Physical Downlink Control Channel) to the terminal to allow theterminal to appropriately receive a RACH response or a RACH MSG 2. Here,the information of the PDCCH may include information of the terminalthat needs to receive the PDSCH including the RACH response or the RACHMSG 2, the frequencies of the radio resources of the PDSCH, thetransmission format of the PDSCH, and the like.

If the terminal successfully receives the PDCCH, the random accessresponse or the RACH MSG 2 transmitted through the PDSCH can beappropriately received according to the information of the PDCCH (S130).Here, the random access response may include a random access preambleidentifier (ID), a UL Grant (uplink radio resources), a temporary C-RNTI(Radio Network Temporary Identifier), a Time Alignment Command (timesynchronization correction value), and the like.

When the terminal receives the random access response or the RACH MSG 2,the information included in the random access response are individuallyprocessed. Namely, the Time Alignment Command is applied, and the C-RNTIis stored.

Also, the terminal uses the UL Grant to transmit the uplink data (MACPDUs or RACH MSG 3) in the MAC layer to the base station (S140).

Thereafter, the MAC layer in the terminal checks whether a NACK signalis received from the base station (S150). If a NACK signal is received,the MAC layer in the terminal uses the common maximum number oftransmissions to retransmit the uplink data (S150).

FIG. 8 shows an exemplary flow chart of the contention based randomaccess procedure between the terminal and the base station.

As can be understood, when the terminal 100 is in RRC Idle Mode, if datais transmitted in the uplink direction (i.e. from terminal 100 to basestation eNB 200), the common value for maximum number of transmissionsis used. Also, if the terminal 100 performs contention based RACHprocedures, the common value for maximum number of transmission is usedin order to transmit the RACH MSG 3. These steps will be described inmore detail below:

1) First, if the terminal 100 is in RRC Idle Mode, a single randomaccess preamble is randomly selected among a set of random accesspreambles based on an indication provided in system information or ahandover command, then the PRACH resources that can be used to transmitthe selected random access preamble are selected, and transmission isperformed. Here, the preamble is called a RACH MSG 1. When the terminalitself selects the preamble in a random manner, such is called acontention based RACH procedure, and the selected preamble is called acontention based preamble.

2) After the terminal 100 transmits the random access preamble,reception of a random access response from the base station 200 isattempted.

In more detail, random access response information (referred to as RACHMSG 2) is transmitted in the form of a MAC PDU (Protocol Data Unit), andsuch MAC PDU is transferred via a PDSCH (Physical Downlink SharedChannel). Also, in order to allow the terminal 100 to appropriatelyreceive the information transferred via the PDSCH, the base station 200also sends control information to the terminal 100 via the PDCCH(Physical Downlink Control Channel). Namely, the information of thePDCCH may include information about the terminal that needs to receivethe PDSCH, the frequency and time information about the radio resourcesfor the PDSCH, the PDSCH transmission format, and the like.

3) If the terminal 100 succeeds in receiving the PDCCH, the randomaccess response transmitted via the PDSCH is appropriately receivedaccording to the information of the PDSCH. Here, the random accessresponse may include a random access preamble identifier (ID), a ULGrant (uplink radio resources), a temporary C-RNTI (Radio NetworkTemporary Identifier), a Time Alignment Commend (time synchronizationcorrection value), and the like.

4) When the terminal 100 has received a valid random access response,the UL Grant is used to transmit data stored in a buffer of the terminalor newly generated data to the base station. Here, the data (i.e. MACPDU) transmitted through the UL Grant is commonly referred to as theRACH MSG 3, and such data (MAC PDU or RACH MSG 3) includes an identifierof the terminal.

5) After the terminal 100 transmits data that includes its identifierusing the UL Grant that was included in the random access response, inorder to resolve any collisions, instructions from the base station 200are awaited. Namely, the PDCCH reception is attempted in order toreceive a particular message.

6) If the terminal 100 receives a NACK signal from the base station 200,the terminal 100 uses the common value for maximum number oftransmissions of HARQ and retransmits the data (i.e. MAC PDU or RACH MSG3). Such retransmission is repeated until the maximum number oftransmissions is reached or until ACk is received. The common maximumnumber of transmissions may be received via an SIB as previouslydescribed.

7) Thereafter, when the terminal 100 enters its RRC Connected Mode, theuplink data are transmitted using the dedicated value for maximum numberof transmissions.

FIG. 9 shows an exemplary flow chart of a contention based random accessprocedure between a terminal and base station.

As can be understood, even if the terminal 100 is in RRC Connected Mode,the common value for maximum number of transmissions is used whencontention based RACH procedures are performed.

Namely, when the terminal 100 enters RRC Connected Mode, even if adedicated value for maximum number of transmissions is received throughdedicated RRC signaling, if the terminal 100 performs contention basedRACH procedures, and because the base station 200 cannot know whichterminal attempted transmissions, the terminal 100 uses the common valuefor maximum number of transmissions.

In contrast, when the terminal 100 performs non-contention based RACHprocedures based upon a dedicated preamble, because the base station 200can know which terminal attempted transmissions, the terminal 100 usesthe dedicated value for maximum number of transmissions. Namely, afterthe terminal transmits a dedicated preamble to the base station, is aRACH MSG 2 is received, the radio resources allocated through the RACHMSS 2 are used, or later allocated radio resources are employed in orderto use the dedicated value for maximum number of transmissions for HARQwhen transmitted data.

The common value for maximum number of transmissions can be receivedfrom the base station via system information, and for contention basedRACH procedures, the common value for maximum number of transmission canbe used in transmitting the RACH MSG 3.

Meanwhile, for non-contention based RACH procedures, the dedicate valuefor maximum number of transmissions of HARQ for UL-SCH transmission canbe used after receiving a RACH response message that includes a responsefor the dedicated preamble.

The exemplary embodiments of the present invention described thus farmay be modified in the following manner.

To increase the efficiency of the HARQ operation, the characteristics ofthe RACH preamble group may be considered. With respect to the actualRACH contention based preamble, by considering the size of the messageto be transmitted by the terminal and considering the amount of powerthat the terminal can use, two RACH preamble groups can be formed. Thus,upon such consideration in the present invention, the base station caninform the terminal of the value for maximum number of transmissionsthat corresponds to each RACH preamble group, and the terminal can usethe value for maximum number of transmissions related to the RACHpreamble group that the terminal is using in order to transmit the RACHMSG 3.

Also, when the base station used the RACH MSG 2 to allocate radioresources, the maximum number of transmissions can be set as desired.Namely, the base station can set the maximum number of transmissions tobe within the limits of the radio resources allocated by the RACH MSG 2.To do so, the base station may additionally include a temporary valuefor maximum number of transmissions into the RACH MSG 2 that is sent tothe terminal. Then, the terminal can use the temporary value for maximumnumber of transmissions to transmit data on the uplink.

Although the concepts about maximum number of transmissions have beendescribed above, the maximum number of re-transmissions may be usedinstead.

The inventive features and characteristics described herein can befurther explained in the following manner:

(1) For a UE in RRC_Connected mode, one common value is used asMAX_NUMBER_OF_ReTX for all HARQ processes/logical channels.

-   -   This is applied to a UL-SCH resources allocated by either        persistent scheduling or dynamic scheduling over PDCCH using        dedicated C-RNtl.

(2) For a UE performing RACH procedure, RACH msg 3 uses UL-SCH and HARQis applied.

-   -   for this UL-SCH resources:        -   MAX_NUMBER_OF_ReTX is informed via System information.            -   this value is applied for RACH msg 3.

(3) For a UE performing RACH procedure, RACH msg 3 uses UL-SCH and HARQis applied.

-   -   for this UL-SCH resources:        -   MAX_NUMBER_OF_ReTX for RACH is informed via System            information.        -   MAX_NUMBER_OF_ReTX for the UE is informed via dedicated RRC            Signaling.            -   if the two MAC_NUMBER_OF_ReTX is same                -   the MAX_NUMBER_OF_ReTX is applied for RACH msg 3.            -   if he two values are different:                -   the value received via system information is                    applied.                -   Or, the value received via dedicated RRC signaling                    is applied.                -   Or, the smaller value of the two is applied.                -   Or, the larger value of the two is applied.                -   Or, the MAX_NUMBER_OF_ReTX is informed via RACH                    message 2. This value is applied for HARQ of RACH                    msg 3.                -   Or, depending on the used RACH preamble Group, each                    RACH preamble group is assigned with a                    MAX_NUMBER_OF_ReTX value.                -    Accordingly, the UE uses the MAX_NUMBER_OF_ReTX                    value associated with the used RACH preamble group                    transmitted at RACH MSG 1.                -    MAX_NUMBER_OF_ReTX value for each RACH preamble                    group is indicated via system information.

The inventive features and characteristics described herein can also befurther explained in the following manner:

For the HARQ operation, the terminal (or UE) may be configured with amaximum number of transmissions that is identical across all HARQProcesses and all logical channels.

In addition, the configuration of “maximum number of transmissions” isdone by RRC signaling. Thus, when the base station (i.e. eNB) allocatesUL-SCH resources to a specific UE, the eNB knows what the maximum numberof transmission is for the allocated radio resources.

But for the case of RACH message 3 (RACH msg 3), it may not bestraight-forward for the eNB to know what the maximum number oftransmission is for the allocated radio resources for RACH msg 3. Thisis because the eNB may not know to which UE the radio resource isallocated.

As such, the following five (5) situations can be considered:

(1) Idle Mode UE

RACH can be used when a UE moves from RRC_IDLE mode to RRC_CONNECTEDmode. Also, RACH can be used while the UE is in RRC_CONNECTED mode.

Until RRC connection is established, the UE is not given any dedicatedconfiguration information. Thus, the value for “maximum number ofretransmission” should be given by other means. One simple way is to useSystem Information (SI). Or, using a pre-defined default value can beconsidered.

But, regardless of whether the default value approach is used or not,the System Information (SI) approach should be adopted as a fallbackmechanism for the case where default value is not appropriate.

Proposal 1: For RACH MSG 3 transmission, RRC_IDLE mode UE applies thevalue received via system information for the “maximum number oftransmission”.

(2) Contention-Based Vs. Non-Contention-Based

In case of contention-based RACH, even if a UE is in RRC Connected modeand received a value for “maximum number of transmission” via dedicatedRRC signaling, the UE should not used this value for the transmission ofRACH MSG 3. This is because the eNB does not know which UE istransmitting over the allocated UL-SCH until contention resolution isover.

While an eNB does not know which UE is transmitting in case ofcontention-based RACH, the eNB can know which UE is transmitting in caseof non-contention based RACH. Thus, if a UE is allocated with adedicated preamble, there is basically no need for the UE to use adefault value.

In fact, in case of non-contention based RACH procedure, the RACHprocedure can be considered as successful when a UE identifies apreamble within a RACH Response message. Then, the RACH message 3transmission is a normal UL-SCH transmission. In this sense, fornon-contention based RACH, a configured value for the UE is used for the“maximum number of transmission” value for the RACH message 3.

Proposal 2: In case of contention-based RACH, “maximum number oftransmission” received over System Information is used for thetransmission of RACH MSG 3. Namely, the value configured by dedicatedRRC signaling is not used.

Proposal 3: In case of non-contention-based RACH, “maximum number oftransmission” value configured for the UE for UL-SCH transmission isused after reception of RACH Response MSG that includes response for theused dedicated preamble.

(3) Group 1 Vs Group 2

In case of contention based RACH procedure, usable preambles areclassified into two groups. The selection of group depends on radioconditions or the size of the message to be transmitted.

When eNB allocates a UL-SCH resource for RACH MSG 3, there can bevarious approaches. For example, the eNB may set different TB (transportblock) sizes, and HARQ operation points such as “maximum number oftransmission” for each group. Or to increase success rate when a UElocated at a cell edge selects a preamble group which allows smallermessage size, the eNB may set a bigger value for “maximum number oftransmission” for the preamble group than the other group(s).

Thus, signaling support to set different values for each group should beadopted.

Proposal 4: The values for “maximum number of transmission” areseparately signaled for each preamble group.

(4) Default Value for SRB1

Proposal 1: Provide default value for Maximum Number of UL transmissionsto be used by the UE for SRB1.

Here, the same value of “maximum number of UL transmission” may apply toall radio bearers. If a default value for “maximum number of ULtransmission” is needed, it is not for SRB1 but for all radio bearers.However, it should be clarified whether a default value exists for“maximum number of UL transmission” or not.

Proposal 5: It is proposed whether default value exist for “maximumnumber of transmission.” If needed, it is used for all radio bearers(RBs).

(5) Dedicated Preamble Case

When an eNB allocates a dedicated RACH preamble to a UE, it alsoindicates the value of “maximum number of UL transmission.” This valueis used and can be informed via system information or via PDCCH whichallocates a dedicated preamble.

When an eNB sends a RACH Response message, it can optionally include avalue for “maximum number of UL transmission.” This value can beincluded per preamble or per message. In case of per-preambleallocation, the UE which is related to the preamble should use the valuefor HARQ. In case of per-message allocation, the all the UE whosepreamble transmission is acknowledged in the message should used thevalue for HARQ.

Only the first HARQ transmission, i.e, for the transmission of RACHmessage 3, the received value for “maximum number of transmission” isused. After that, normal value which is configured per UE or the valuereceived SIB is used.

The features and characteristics described herein can be furtherexplained in the following manner:

Among various MAC procedures, the Random Access procedure involves aRandom Access Procedure initialization and Random Access Responsereception.

The Random Access procedure can be initiated by a PDCCH order or by theMAC sublayer itself. The PDCCH order or RRC optionally indicates aRandom Access Preamble and PRACH resource.

Before the procedure can be initiated, the following information isassumed to be available:

-   -   the parameter: Maximum number of Msg3 HARQ transmissions Once        the Random Access Preamble is transmitted and regardless of the        possible occurrence of a measurement gap, the UE shall monitor        the PDCCH for Random Access Response(s) identified by the        RA-RNTI defined below, in the TTI window        [RA_WINDOW_BEGIN-RA_WINDOW_END] which starts at the subframe        that contains the end of the preamble transmission [7] plus        three subframes and has length ra-ResponseWindowSize subframes.        The RA-RNTI associated with the PRACH in which the Random Access        Preamble is transmitted, is computed as:        RA-RNTI=t _(—) id+10*f _(—) id

where t_id is the index of the first subframe of the specified PRACH(0≦t_id<10), and f_id is the index of the specified PRACH within thatsubframe, in ascending order of frequency domain (0≦f_id<6).

The UE may stop monitoring for Random Access Response(s) aftersuccessful reception of a Random Access Response containing RandomAccess Preamble identifiers that matches the transmitted Random AccessPreamble.

-   -   If a downlink assignment for this TTI has been received on the        PDCCH for the RA-RNTI and the received TB is successfully        decoded, the UE shall regardless of the possible occurrence of a        measurement gap:    -   if the Random Access Response contains a Backoff Indicator        subheader:    -   set the backoff parameter value in the UE as indicated by the BI        field of the Backoff Indicator subheader and Table 7.2-1.    -   else, set the backoff parameter value in the UE to 0 ms.    -   if the Random Access Response contains a Random Access Preamble        identifier corresponding to the transmitted Random Access        Preamble (see subclause 5.1.3), the UE shall:    -   consider this Random Access Response reception successful;    -   process the received Timing Advance Command (see subclause 5.2);    -   indicate the amount of power ramping applied to the latest        preamble transmission to lower layers (i.e.,        (PREAMBLE_TRANSMISSION_COUNTER-1)*POWER_RAMP_STEP);    -   process the received UL grant value and indicate it to the lower        layers;    -   if the Random Access Preamble was explicitly signalled and the        signalled random access preamble ID was not 000000 (i.e., not        selected by MAC):    -   consider the Random Access procedure successfully completed.    -   else, if the Random Access Preamble was selected by UE MAC:    -   set the Temporary C-RNTI to the value received in the Random        Access Response message no later than at the time of the first        transmission corresponding to the UL grant provided in the        Random Access Response message;    -   if this is the first successfully received Random Access        Response within this Random Access procedure:    -   if the transmission is not being made for the CCCH logical        channel, indicate to the Multiplexing and assembly entity to        include a C-RNTI MAC control element in the subsequent uplink        transmission;    -   obtain the MAC PDU to transmit from the “Multiplexing and        assembly” entity and store it in the Msg3 buffer.

It should be noted that when an uplink transmission is required, e.g.,for contention resolution, the eNB should not provide a grant smallerthan 80 bits in the Random Access Response.

Also, it should be noted that if within a Random Access procedure, anuplink grant provided in the Random Access Response for the same groupof Random Access Preambles has a different size than the first uplinkgrant allocated during that Random Access procedure, the UE behavior isnot defined.

Regarding the HARQ process, each HARQ process is associated with a HARQbuffer. Each HARQ process shall maintain a state variable CURRENT_TX_NB,which indicates the number of transmissions that have taken place forthe MAC PDU currently in the buffer, and a state variable HARQ_FEEDBACK,which indicates the HARQ feedback for the MAC PDU currently in thebuffer. When the HARQ process is established, CURRENT_TX_NB shall beinitialized to 0.

The sequence of redundancy versions is 0, 2, 3, 1. The variableCURRENT_IRV is an index into the sequence of redundancy versions. Thisvariable is up-dated modulo 4.

New transmissions and adaptive retransmissions are performed on theresource and with the MCS indicated on PDCCH, except for newtransmissions of Msg3 which are performed according to UL grant inRandom Access Response. Non-adaptive retransmission is performed on thesame resource and with the same MCS as was used for the last madetransmission attempt,

The UE is configured with a Maximum number of HARQ transmissions and aMaximum number of Msg3 HARQ transmissions by RRC. For transmissions onall HARQ processes and all logical channels except for transmission of aMAC PDU stored in the Msg3 buffer, maximum number of transmissions shallbe set to Maximum number of HARQ transmissions. For transmission of aMAC PDU stored in the Msg3 buffer, maximum number of transmissions shallbe set to Maximum number of Msg3 HARQ transmissions.

Regarding MAC-Main Configuration field descriptions, a “maxHARQ-Tx” mayhave a parameter: max-HARQ-Tx. If such is absent in theRRCConnectionSetup message, a pre-defined default value may be used.

Regarding RACH-ConfigCommon field descriptions, a “maxHARQ-Msg3Tx” mayhave a parameter: max-HARQ-Msg3-Tx. Such can be used for contentionbased random access, and this value is an integer.

The present invention provides a method of performing a random accessprocedure by a terminal. Such method may be performed for an LTE system,a UMTS system, or the like. The steps of transmitting a random accesspreamble to a base station, receiving a random access response from thebase station, and performing an uplink transmission using an uplinkgrant from the base station, are performed, wherein the uplinktransmission is performed by using a maximum number of HARQ (HybridAutomatic Repeat reQuest) transmissions parameter, which is included ina System Information Block (SIB) received from the base station.

Here, the uplink grant may be included in the received random accessresponse. The random access preamble may have been selected at a MAC(Medium Access Control) layer in the terminal. The uplink transmissionmay include a mobile terminal identifier and the uplink grant is relatedto HARQ information. The uplink grant and the HARQ information may bereceived from a lower layer with respect to the MAC layer. The randomaccess response may trigger a generation of a message that istemporarily stored and wherein the maximum number of HARQ transmissionsparameter is used in deciding when to flush a HARQ buffer in theterminal.

The present invention also provides a terminal comprising an RRC (RadioResource Control) layer configured to receive maximum number of HARQ(Hybrid Automatic Repeat reQuest) transmissions parameters via systeminformation or via a dedicated massage, and a MAC (Medium AccessControl) layer configured to receive two kinds of maximum number of HARQtransmissions parameters from the RRC layer, wherein a first kind ofmaximum number of HARQ transmissions parameter is used for transmissionof data related to a RACH procedure, and a second kind of maximum numberof HARQ transmissions parameter is used for other types oftransmissions.

Here, the transmission of data related to the RACH procedure may use aRACH MSG3 message. The first kind of maximum number of HARQtransmissions parameter is received via the system information, and thesecond kind of maximum number of HARQ transmission parameter is receivedvia the dedicated message. The transmission of data related to the RACHprocedure is defined as an uplink transmission using an uplink grantreceived in a RACH access response. The RACH access response triggers ageneration of a message, which is temporarily stored. Here, a MSG 3 maybe stored in a so-called MSG3 buffer. The maximum number of HARQtransmissions parameter is used in deciding when to flush a HARQ bufferin the terminal. A Maximum number of HARQ transmissions and a Maximumnumber of Msg3 HARQ transmissions are configured by the RRC layer. Fortransmissions on all HARQ processes and all logical channels except fortransmission of a MAC PDU stored in a Msg3 buffer, a maximum number oftransmissions shall be set to Maximum number of HARQ transmissions. Fortransmission of a MAC PDU stored in a Msg3 buffer, a maximum number oftransmissions shall be set to Maximum number of Msg3 HARQ transmissions.

The features described herein can be applied to the so-called LTE (LongTerm Evolution) technologies, which are being developed after 3G mobilecommunications in anticipation of rapidly increasing data traffic. Suchis one aspect of developing an evolved network that can support greaterbandwidth, and the term E-UTRAN (Evolved UTRAN) is being used.

However, the features and characteristics described herein are not meantto be limited to LTE, but can also be adapted, applied and implementedin various other communication systems and methods, such as GSM, GPRS,CDMA, CDMA2000, WCDMA, IEEE 802.xx, UMTS, etc.

The method of the present invention explained thus far can beimplemented in software, hardware, or a combination thereof. Forexample, the method of the present invention can be implemented as codesor commands of a software program that can be executed by a processor(CPU), and can be saved in a storage medium (e.g. memory, hard disk,etc.).

Certain aspects for the method of the present invention may beimplemented in a mobile terminal or network entity (such as the RNC orNode B of FIG. 1). The mobile terminal or network entity may include theprotocols of FIGS. 2 and 3, as can be understood by those skilled in theart.

Thus far, some exemplary embodiments of the present invention have beendescribed, but such embodiments are not meant to limit the featuresdescribed herein. As such, all reasonable and various modifications,changes, improvement and variations are part of the present invention.

INDUSTRIAL APPLICABILITY

The features and concepts herein are applicable to and can beimplemented in various types of user devices (e.g., mobile terminals,handsets, wireless communication devices, etc.) and/or network entitiesthat can be configured to support a method for performing random accessprocedures.

As the various concepts and features described herein may be embodied inseveral forms without departing from the characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsscope as defined in the appended claims. Therefore, all changes andmodifications that fall within such scope or equivalents thereof aretherefore intended to be embraced by the appended claims.

1. A method of performing a random access procedure by a terminal, themethod comprising: setting two kinds of maximum number of HybridAutomatic Repeat reQuest (HARQ) transmissions parameter, wherein a firstkind of maximum number of HARQ transmissions parameter is used fortransmitting an uplink data according to Random Access Channel (RACH)procedure and a second kind of maximum number of HARQ transmissionsparameter is used for transmitting data other than Protocol Data Unit(MAC PDU) stored in a MSG3 buffer; transmitting a random access preamblewhich is selected at a Medium Access Control (MAC) layer in theterminal; receiving a random access response in response to transmittingthe random access preamble; and performing an uplink transmission usingan uplink grant included in the random access response, wherein theuplink data includes an identifier of the terminal and the uplink datatransmitted using the uplink grant is a MAC PDU, and wherein the uplinktransmission is performed by using the first kind of maximum number ofHARQ transmissions parameter, which is included in a System InformationBlock (SIB) received from a base station.
 2. The method of claim 1,wherein the uplink grant is received from a lower layer and informationon the first kind of the maximum number of HARQ transmissions parameteris received from the lower layer.
 3. The method of claim 1, wherein theuplink data is RACH MSG3.
 4. The method of claim 1, wherein the randomaccess response triggers generation of RACH MSG3 related to the uplinkdata.
 5. The method of claim 4, wherein the triggered RACH MSG3 istemporally stored within the MSG3 buffer.
 6. The method of claim 1,wherein the first type of the maximum number of HARQ transmissionsparameter is a max-HARQ-Msg3Tx parameter.
 7. A terminal comprising: ARadio Resource Control (RRC)) layer configured to receive two kinds ofmaximum number of Hybrid Automatic Repeat reQuest (HARQ) transmissionsparameters via system information or via a dedicated massage; and aMedium Access Control (MAC) layer configured to receive the two kinds ofmaximum number of HARQ transmissions parameters from the RRC layer,wherein a first kind of maximum number of HARQ transmissions parameteris used for transmission of data related to a RACH procedure, and asecond kind of maximum number of HARQ transmissions parameter is usedfor transmission of data other than Protocol Data Unit (MAC PDU) storedin a MSG3 buffer.
 8. The terminal of claim 7, wherein the transmissionof data related to the RACH procedure uses a RACH MSG3 message.
 9. Theterminal of claim 7, wherein the first kind of maximum number of HARQtransmissions parameter is received via the system information, and thesecond kind of maximum number of HARQ transmission parameter is receivedvia the dedicated message.
 10. The terminal of claim 7, wherein thetransmission of data related to the RACH procedure is defined as anuplink transmission using an uplink grant received in a RACH accessresponse.
 11. The terminal of claim 10, wherein the RACH access responsetriggers generation of RACH MSG3, which is temporarily stored.
 12. Theterminal of claim 11, wherein the triggered RACH MSG3 is temporallystored in the MSG3 buffer.
 13. The terminal of claim 7, wherein themaximum number of HARQ transmissions parameter is used for determiningwhen to flush a HARQ buffer in the terminal.
 14. The terminal claim 7,wherein the first type of the maximum number of HARQ transmissionsparameter is a max-HARQ-Msg3Tx parameter.
 15. The terminal claim 7,wherein the second type of the maximum number of HARQ transmissionsparameter is maxHARQ-TX.